Fluorine separation and generation device

ABSTRACT

A process and apparatus for the electrolytic separation of fluorine from a mixture of gases is disclosed. Also described is the process and apparatus for the generation of fluorine from fluorine/fluoride containing solids, liquids or gases.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to application Ser. No. 60/416,309,filed Oct. 4, 2002, the contents of which are hereby incorporated byreference in their entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under Grant (Contract)No. DE-AC03-76F00098 awarded by The United States Department of Energy.The government has certain rights to this invention.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of fluorineseparation and fluorine generation devices, and more particularly to anovel electrolytic device having unusual and unexpected electrochemicalperformance.

The semiconductor industry makes extensive use of gas mixtures thatcontain fluorine. Many of these substances are harmful and expensive,and must therefore be removed or scrubbed from the exhaust gas stream.Accordingly a need exists for a device and method to separate fluorinefrom gas mixtures, and to generate the fluorine needed for the industry.

There are several approaches to separate fluorine (F₂) from other gases,including cryogenic distillation, permeation membranes, and electrolyticseparation. Electrolytic separation offers the potential advantages ofproducing high purity fluorine at room temperature at high flux in acompact unit. Methods are known for the electrochemical separation ofgas mixtures. One technique, described in U.S. Pat. No. 5,618,405teaches the separation of halides from high temperature gas mixturesusing an electrochemical cell, the contents of which are herebyincorporated by reference in its entirety. Another technique known asthe “outer-cell” method the gaseous component of a waste gas to bestripped are first absorbed in an absorption column in a wash solution;then the wash solution containing the polluting component iscathodically reduced or anodically oxidized in a connected electrolysiscell. This arrangement requires two different devices, namely one forthe absorption and one for the electrolysis. Another technique is the“inner-cell” method in which absorption and electrochemical conversiontake place in an electrolysis cell, and because the concentration ofpollutants is always kept low by electrochemical conversion. Yet anothermethod is the “indirect” electrolysis processes where the oxidizing orreducing agent used in a wet-chemical waste-gas treatment is regeneratedby electrolysis of the wash solution used.

U.S. Pat. Nos. 6,071,401 and 5,840,174, the contents of which areincorporated herein by reference in their entirety disclose anelectrolysis cell with a fixed-bed electrode for the purification ofwaste gases. In reductive purification hydrogen is supplied to the gasdiffusion electrode and in oxidative purification oxygen is used.

U.S. Pat. No. 6,030,591, the contents of which are incorporated hereinby reference in their entirety discloses the separation offluorocompounds by cryogenic processing, membrane separation and/oradsorption.

U.S. Pat. Nos. 6,514,314 and 5,820,655, the contents of which areincorporated herein by reference in their entirety disclose a ceramicmembrane structure an oxygen separation method.

One disadvantage of the inner cell method is the high residual contentof impurities in the purified gas. In the case of chlorine the residualcontent is approximately a factor of ten above the limit value of 5 ppm.In general, the purity of gases generated by solid state devices is muchhigher than that of liquid (or melt) containing cells.

Another disadvantage of the prior art methods is the fact that theapparatus comprising an electrolysis cell requires two liquid circuits,namely a cathode circuit and an anode circuit, as a result of which thedevice is rendered complicated and trouble-prone.

Solid-state electrochemical devices are often implemented as cellsincluding two porous electrodes, the anode and the cathode, and a densesolid electrolyte and/or membrane, which separate the electrodes. Forthe purposes of this application, unless otherwise explicit or clearfrom the context in which it is used, the term “electrolyte” should beunderstood to include solid oxide membranes used in electrochemicaldevices, whether or not potential is applied or developed across themduring operation of the device. In many implementations the solidmembrane is an electrolyte composed of a material capable of conductingionic species, such as fluorine ions, yet has a low electronicconductivity. In other implementations, such as gas separation devices,the solid membrane may be composed of a mixed ionic electronicconducting material (“MIEC”). In each case, the electrolyte/membranemust be dense and as pinhole free as possible (“gas-tight”) to preventmixing of the electrochemical reactants. In all of these devices a lowertotal internal resistance of the cell improves performance.

Solid-state electrochemical devices are typically based onelectrochemical cells with ceramic electrodes and electrolytes and havetwo basic designs: tubular and planar. Tubular designs havetraditionally been more easily implemented than planar designs, and thushave been proposed for commercial applications. However, tubular designsprovide less power density than planar designs due to their inherentlyrelatively long current path that results in substantial resistive powerloss. Planar designs are theoretically more efficient than tubulardesigns, but are generally recognized as having significant safety andreliability issues due to the complexity of sealing and manifolding aplanar stack.

SUMMARY OF THE INVENTION

The present invention describes an electrolytic cell for theelectrolytic removal of fluorine from gas mixtures. Another object ofthe present invention is the separation of fluorine fromfluorine/fluoride containing sources (gases, liquids or solids), such asHF, NF₃, CF₄, SF₆, etc. The present invention describes the electrolyticcell to accomplish the aforementioned and novel methods for makingimproved cells over the prior art. These and other features andadvantages of the present invention will be presented in more detail inthe following specification of the invention and the accompanyingfigures, which illustrate by way of example the principles of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawing:

FIG. 1 depicts a planar design solid state electrochemical device of theprior art.

FIG. 2 depicts a fluorine separation device in accordance with oneembodiment of the present invention.

FIG. 3 depicts a fluorine separation device in accordance with oneembodiment of the present invention

FIG. 4 shows the curent/voltage relationship for Pt electrodes.

FIG. 5 shows the current/voltage relationship for Pt electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to some specific embodiments of theinvention. Some examples of these specific embodiments are illustratedin the accompanying drawings. While the invention is described inconjunction with these specific embodiments, it will be understood thatit is not intended to limit the invention to the described embodiments.On the contrary, it is intended to cover alternatives, modifications,and equivalents as may be included within the spirit and scope of theinvention as defined by the appended claims. In the followingdescription, numerous specific details are set forth in order to providea thorough understanding of the present invention. The present inventionmay be practiced without some or all of these specific details. In otherinstances, well known process operations have not been described indetail in order not to unnecessarily obscure the present invention.

In this specification and the appended claims, the singular forms “a,”“an,” and “the” include plural reference unless the context clearlydictates otherwise. Unless defined otherwise, all technical andscientific terms used herein have the same meaning as commonlyunderstood to one of ordinary skill in the art to which this inventionbelongs.

Introduction

An overview of solid-state device components and construction follows.This description is provided both by way of background and introductionto the subject, and to provide design and fabrication details that maybe adopted in compositions, devices, and methods in accordance with thepresent invention.

While the designs depicted and described in FIG. 1 is intended for useas a solid oxide fuel cell (SOFC) the same or a similar device designsis also used for fluorine separation is useful depending on theselection of materials used as the electrodes and separators, theenvironment in which the device is operated (gases supplied at eachelectrode), pressures or electrical potentials applied, and theoperation of the device. For example, as described above, for a fuelcell, a hydrogen-based fuel (typically methane that is reformed tohydrogen during operation of the device) is provided at the fuelelectrode and air is provided at the air electrode. Oxygen ions (O²⁻)formed at the air electrode/electrolyte interface migrate through theelectrolyte and react with the hydrogen at the fuelelectrode/electrolyte interface to form water, thereby releasingelectrical energy that is collected by the interconnect/currentcollector.

FIG. 1 illustrates a basic planar design for a solid-stateelectrochemical device, for example, a solid oxide fuel cell (SOFC). Thecell 100 includes an anode 102 (the “fuel electrode”) and a cathode 104(the “air electrode”) and a solid electrolyte 106 separating the twoelectrodes. In conventional SOFCs, the electrodes and electrolytes aretypically formed from ceramic materials, since ceramics are able towithstand the high temperatures at which the devices are operated. Forexample, SOFCs are conventionally operated at about 950° C. Thisoperating temperature is determined by a number of factors, inparticular, the temperature required for the reformation of methane toproduce hydrogen and reaction efficiency considerations. Also, typicalsolid-state ionic devices such as SOFCs have a structural element ontowhich the SOFC is built. In conventional planar SOFCs the structuralelement is a thick solid electrolyte plate; the porous electrodes arethen screen-printed onto the electrolyte. The porous electrodes are oflow strength and are not highly conductive. Alternatively, a thickporous electrode and a thin electrolyte membrane can be co-fired,yielding an electrode/electrolyte bilayer.

Another consideration governing the temperature at which the solid-stateelectrochemical device described herein is operated is theelectrolyte/membrane conductivity. Conventional devices must be operatedat a high enough temperature to make the ceramic electrolytesufficiently ionically conductive for the energy producing reactions (inthe case of a SOFC; other reactions for gas separators or generators).

Typical devices described in accordance with the present inventionoperate at temperatures of approximately 120° C., but that temperatureranges from between 100-300° C., and preferably between 120-150° C.,depending partially upon the choice of electrolyte. For the preferredelectrolyte of PbSnF₄, the operating temperature is about 120° C. Foranother electrolyte, such as LaF₃ the temperature is between 300-500°C., because of the conductivity of the LaF₃. If the electrolytic cell isrun at a temperature of less than 150° C., a teflon or teflon basedmaterial may be used in the device, for seals and the like.

Methods exist for forming thin electrolytes on substrates, such asEVD/CVD. However, EVD/CVD is a complex and expensive technique, and theceramic-based devices to which the technique has been applied stillrequire high operating temperatures to be at all efficient.Unfortunately, most metals are not stable at this temperature in anoxidizing environment and very quickly become converted to brittleoxides. The present invention contemplates sputtering as a method offorming thin film electrolytes on substrates. Sputtering contemplated bythis method is taught in the art, see for instance P. Hagenmuller, A.Levasseur, C. Lucat, J. M. Reau, and G. Villeneuve, in “Fast iontransport in solids. Electrodes and electrolytes. North-Holland. 1979,pp. 637-42. Amsterdam, Netherlands.” (P. Vashishta, J. N. Mundy, and G.K. Shenoy, eds.), 1979, the contents of which are hereby incorporated byreference in its entirety. Films made using this method generally willbe thin, less than about 1 micron.

This invention contemplates a preferred method for making electrolytefilm having a thickness of between 10-50 microns by melting as describedbelow in Example 1.

Referring again to FIG. 1, the cell 100 is depicted in the form in whichit could be stacked with other like cells 110, as it typically would beto increase the capacity of the device. This embodiment is contemplatedin the present invention. To be stacked, the cells require bipolarinterconnects 108 adjacent to each electrode that are electrically, butnot ionically, conductive, in the present invention. In the presentinvention, the interconnects 108 allow current generated in the cells toflow between cells and be collected for use. These interconnects aretypically formed into manifolds through which the source gas and carriergas may be supplied to the respective electrodes (allow lateral movementof gas in channels; but not allow intermixing of gas (verticalmovement). Due to the corrosive nature of F₂, materials for theinterconnect must be corrosion resistant. Teflon and teflon basedmaterials are contemplated. The interconnect may also be a F₂ corrosionresistant materials such as Ni or a Ni alloy, or, preferably, stainlesssteel. Electrically conductive interconnects in the present inventionmay be used to separate the anode and cathode chambers and to applycurrent to the electrodes. Aluminum and aluminum alloys may be used ifthe device of the present invention is to be operated at or below 300°C. The choice of interconnect material is readily determinable by one ofordinary skill depending on the temperatures of use.

The electrode materials may be different between cathode and anode.Preferably, the anode material should have a low overpotential forelectrochemical fluorine generation, and the cathode should have a highoverpotential for electrolyte reduction, i.e. electrodeposition of Pband Sn, if PbSnF₄ is used. Pt is most preferred for the anode, andgraphite the most preferred for the cathode. The overpotential is theapplied potential less the initial or equilibrium potential and the IRdrop on the electrolyte. In operation the reference electrode may not benecessary, and one having skill in the art will be able to optimize theoverpotential for any particular electrolyte. This value will enableoperation of the device inside the potential range or stability windowfor the particular electrolyte chosen. Of course, one of ordinary skillwill readily appreciate that operating the device at too high apotential will create to much current and destroy the electrolyte. Thepresent invention contemplates that a device operating with a PbSnF₄electrolyte and Sn/SnF₂ reference electrodes, the window would beapproximately 0 to about 5-6 volts, vs Sn/SnF₂ reference.

The electrodes (anode and cathode) used in accordance with the fluorinegeneration or separation device described herein are preferablymaterials which do not produce highly volatile or electricallyinsulating fluorides in and under the electrical potentials applied tothe device. Importantly, electrode materials must be chosen that do nothave adverse reactions with the thin-film electrolyte. Non-limitingexamples are metals such as platinum, gold, nickel, palladium, copper,silver, alloys of these metals, and graphitic carbon. A preferredmaterial for the cathode is carbon, preferably graphitic carbon. Apreferred material for the anode is Pt. One having skill in the art willappreciate that the anode and cathode may both be of the same material,depending on the choice of electrolyte.

In a preferred embodiment of the electrode, there is contemplated atriple phase boundry with a high surface area of the electrolytematerial, the electrode material and the gas being used in the gasseparation or generation device. This is accomplished by providing smallparticles (high surface area) of Pt powder, i.e. Pt black (0.05 micronsto 20 microns, preferably 0.7 microns to 2 microns) and pressing at 1000psi. During operation, all three phases are interpenetrating, resultingin three phase boundaries throughout.

In another embodiment of the present invention there is contemplated acarbon electrode. This may be prepared from petroleum cokes containingcoal tar pitch as binder. Preferably the carbon anode is formed with 40wt % of coal tar pitch as a binder, which will lead to the increase inthe effective internal surface due to the proper size and distributionof pores on the carbon anode. Similar anodes are known in the art anddescribed in Ahn et al. Journal of the Korean Chemical Society, 2001,Vol. 45, No. 5, the contents of which are hereby incorporated byreference in its entirety for all purposes.

In order to separate fluorine efficiently from impurity gases byelectrolysis, it is preferable to have a dense membrane that isconductive to fluoride ion, with reasonably high ionic conductivity atambient or slightly elevated temperatures. Such materials are known. Twonon-limiting examples are PbSnF₄ and LaF₃, which both have high ionicconductivity for fluoride ion. The ionic conductivity of PbSnF₄ is about10⁻³ Ω⁻¹ cm⁻¹ at room temperature; therefore resistivity (ρ) is 10³ Ωcmat room temperature. Using the relationship R=ρ(length/Area), thenR=1000 (length/1 cm²). For a PbSnF₄ plate of 1 mm thickness, AreaSpecific Resistance (R·Area)=100 Ωcm²; if we decrease the thickness ofthe electrolyte to 10 microns, then ASR=1 Ωcm² at room temperature. Thismeans that in a device run at a current density of 1 amp/cm², theelectrolyte resistance will only contribute 1 volt in iR loss at roomtemperature. There are also other fluoride ion conductors such as LaF₃,which has an ionic conductivity of LaF₃ is 5×10⁻⁵ S/cm at 20° C.

The overpotential of the F₂/F⁻ electrodes as a function of currentdensity is important. In one embodiment of the present invention thereis used use carbon-based electrodes as is done for HF oxidation,however, those electrodes are known to become passivated giving rise tolarge overpotentials. Recently, Groult et al. showed this to be due tothe formation of CF_(x) on the carbon electrode surface which inhibitswetting of the electrode, see H. Groult, D. Devilliers, S. Durand-Vidal,F. Nicolas, and M. Combest, Electrochimica Acta, 44, 2793 (1999), thecontents of which are incorporated herein by reference. The presentinvention is not particularly concerned with wetting of a carbonelectrode with molten KF—HF, so this phenomenon may not be an issue forredox of F₂ mixed with impurity gases. Pletcher showed that theoverpotentials for the F₂/F⁻ redox reaction are much lower on Ptelectrodes than on carbon, see A. G. Doughty, M. Fleischmann, and D.Pletcher, Electroanal. Chem. And Interfacial Electrochem., 51, 329(1974), the contents of which are incorporated herein by reference. Thecurrent voltage relationship for Pt electrodes are shown in the FIGS. 1and 2. Given the low overpotential for F₂ evolution, very lowoverpotentials for porous Pt electrodes having high surface area arepossible.

In one embodiment (FIG. 2) the present invention contemplates a thickPbSnF₄ disk (0.1-2.5 mm, preferably 1-2 mm thick) coated with thin (50microns) Pt/PbSnF₄ composite electrodes. The invention contemplates thatthe electrode thickness may be 2 microns to 100 microns, preferablybetween 10 and 50 microns. A Pt reference electrode can be used tomonitor anode and cathode overpotentials.

In another more preferred embodiment, the fluorine separation andgeneration device contemplates the structure shown in FIG. 3. Here thethickness of the electrolyte is minimized to eliminate iR losses, andthe membrane is supported on a conductive substrate. Preferably, thesubstrate will be a stainless steel porous support onto which aPt/PbSnF₄ slurry is deposited followed by deposition of a dense PbSnF₄film (2-200 μm, preferably ˜10-20 μm) onto which the second Pt/PbSnF₄electrode is deposited. The invention contemplates that the fluorineseparation device is functional when fabricated in flat plates (smallerfootprint device), or a tubular shape (simplified seals). One havingordinary skill will appreciate that other shapes are possible withoutaltering the nature of the invention.

Methods for making the fluorine separation device of the presentinvention are known in the art. The present invention also contemplatesnovel techniques, which produce electrode/electrolyte interfaces havingunexpected superior properties. U.S. Pat. No. 6,605,316, by inventors ofthe present invention describes the structure and fabrication techniquesfor solid state electrochemical devices, the contents of which areincorporated herein by reference. Other pending published applicationsby the inventors of the present invention describe techniques suitablefor constructing the electrochemical device described herein. U.S.Published application No. 2003-0021900 A1 describes a method of makingcrack free dense films; U.S. Published application No. 2003 0175439 A1describes processes for making electrolytic dense films; U.S. Publishedapplication No. 2002-0081762 A1 describes electrolytic structures andprocesses for making. The contents of the above patents and applicationsare hereby incorporated herein by reference for all purposes.Additionally, membrane electrode assemblies useful for the electrolyzersof the present invention are disclosed in U.S. Pat. No. 6,613,106, thecontents of which are incorporated herein by reference in theirentirety.

The electrolyte membrane of the present invention comprises a materialcapable of conducting fluorine. The material must be a solid, and not beporous such that there is no gas movement through the membrane. Theelectrolyte must be gas tight. Preferably the material is PbSnF₄. ThePbF₂/SnF₂ system is very rich in new materials. These include a widePb_(1-x)Sn_(x)F₂ solid solution (0.x.0.50, cubic.-PbF₂ fluorite-type for0.x.0.30, tetragonal.-PbSnF₄ fluorite-type for 0.30<x.0.50) andstoichiometric Pb₂SnF₆, PbSnF₄ and PbSn₄F₁₀. In addition, all thestoichiometric compounds undergo phase transitions on heating. Thesephases are also very high performance fluoride-ion conductors, the bestamong all fluoride ion conductors, with PbSnF₄ being the very best.Ball-milling has been extensively used for oxides and other stronglattices, and it is usually found to lead slowly to amorphization.Ball-milling has also been used to supply the energy required to performsolid state reactions. Surprisingly, the phase transition onball-milling takes place very rapidly (ca. 5 minutes) and noamorphization or further reduction of particle size occurs on furthermilling (checked up to 1 hour). At small x values, a.-PbF₂ like behavioris observed, while for the highest x values, it behaves like.-PbSnF₄,with a slowing down of the transformation as x moves towards the centerof the solid solution, where no change is observed. The particle sizeobtained at a given ball-milling time is a function of the fractionalamount x of tin in the samples.

Other materials contemplated for the electrolyte are LaF₃, doped orundoped with rare earth metals, preferably Er. Other electrolytematerials capable of ionic transfer of fluorine known in the art arealso contemplated as useful for this invention.

In one embodiment of the present invention the electrolyte is a ceramicelectrolyte which is substantially impermeable to the passage of gasesbut permeable to fluoride-ions. An example of such an electrolyte andmethod of making is known in the art. U.S. Pat. No. 4,707,224, thecontents of which are hereby incorporated by reference in its entiretyfor all purposes. An unexpected advantage to the present invention overthis patent is that electrodes was made by sputtering and/or evaporationand there is not a triple phase boundry uniformly present, exceptperhaps in film pinholes and other defects.

Contemplated for the substrate materials for which the structure may beaffixed are porous metals such as the transition metals chromium,silver, copper, iron and nickel, or a porous alloy such as low-chromiumferritic steels, such as type 405 and 409 (11-15% Cr),intermediate-chromium ferritic steels, such as type 430 and 434, (16-18%Cr), high-chromium ferritic steels, such as type 442, 446 and E-Brite(19-30% Cr), chrome-based alloys such as Cr5Fe1Y and chrome-containingnickel-based Inconel alloys including Inconel 600 (Ni 76%, Cr 15.5%, Fe8%, Cu 0.2%, Si 0.2%, Mn 0.5%, and C 0.08%).

In some embodiments of the present invention, the substrate may be aporous cermet incorporating one or more of the transition metals Ni, Cr,Fe, Cu and Ag, or alloys thereof.

A protective layer for either or both electrodes is furthercontemplated. In addition to providing protection for electrolyte, theprotective layer should conduct ions generated during discharge of thenegative electrode. The protective layer may be deposited by sputteringor evaporation. Materials for the protective layer may include alkaliand alkali earth metal fluorides, such as CaF₂, MgF₂ or KF. Also,contemplated by this invention and preferred is doped or undoped LaF₃.This layer will separate the electrode from the electrolyte. Thethickness of the layer is less than 1 micron. These are known in the artand disclosed in U.S. Pat. No. 6,025,094, the contents of which arehereby incorporated in their entirety.

The present invention also contemplates that the solid stateelectrochemical device described herein is also useful as a fluorinegeneration device. In this manner, gasses such as HF, NF₃, CF₄ and SF₆may be electrochemically converted to fluorine gas. The inventioncontemplates that a mixture of gases may also be used as input gases, togenerate fluorine gases. Example 4 describe one embodiment in accordancewith this concept. Also contemplated is the use of liquids (nonlimitingexamples of which include KF*HF melts) and solids (nonlimiting exampleswhich include KF, PBF₂, CoF₃) as input materials. In this embodiment thecathode may be different than the cathode for a fluorine separationdevice dependent on the source of fluorine, but the anode andelectrolyte can be as described for the separation device, because thechemistry is the same. Preferred cathode materials for a fluorinegeneration device are Pt, if one is using as input material NF₃, forexample. One skilled in the art will be able to choose suitablematerials for the cathode material depending on the choice of inputmaterial. The choice is based on minimizing the overpotential for thereaction which is the reduction of gases to fluoride ion F⁻ and aresidual gas (N₂ in the case of NF₃ source gas).

The techniques described herein, and the structures they produce may beused in the fabrication of a variety of electrochemical devices, asdescribed above, to reduce cost, improve performance and reliability,and reduce operating temperature for an efficient device. It should beunderstood that the fabrication techniques and structures describedherein might be implemented in either planar, hexagonal or tubularsolid-state electrochemical device designs.

EXAMPLES

The following examples describe and illustrate aspects and features ofspecific implementations in accordance with the present invention. Itshould be understood the following is representative only, and that theinvention is not limited by the detail set forth in these examples.

Example 1

A thin film electrolyte cell can be prepared by melt solidification. APt—PbSnF₄ powder mixture is uniformly spread on top of a porousstainless steel support and pressed in a die at 1000 PSI to form apressed film of 1-20 microns, preferably 5-10 microns. PbSnF₄ powder isapproximately uniformly spread on the bilayer structure and die pressedat 5000 PSI. The cell is placed in a closed cylinder which can be purgedwith F₂ or F₂ in an inert gas (He, Ar or N₂) and heated to 390° C., themelting point of PbSnF₄. Upon cooling, the electrolyte solidifies to acompact film. The second Pt—PbSnF₄ electrode is sprayed on theelectrolyte film to a thickness of 1-20 microns, preferably 5-10microns.

Example 2

An electrolyte supported cell can be prepared by the following method. Asaturated aqueous solution of Pb(NO₃)₂ is added drop-wise to a saturatedaqueous solution of SnF₂, acidified by 5% HF, under stirring. The whiteprecipitate formed is filtered by vacuum filtration, and dried in vacuumoven at room temperature overnight. The resulted powder is die presseduniaxially at 50 KPSI and room temperature for 5 min. The disc resultedhas an electrical conductivity of 3×10⁻² S/cm at 100° C., measured byimpedance spectroscopy. In a slightly larger die than the diameter ofthe electrolyte disc, Pt or Pt—PbSnF₄ powder mixture, either dry or as apaste in isopropyl alcohol, is spread on both faces of the disc, andpressed at 1000 PSI, to form porous electrodes.

Example 3

Operation of a fluorine separation device in accordance with oneembodiment of this invention. With reference to FIG. 3 (optionalelements are now shown), a membrane electrode assembly may be sandwichedbetween two aluminum blocks (not shown), separated by a Teflon sheet(not shown). Here it is understood in FIG. 3, as well as FIG. 2, that“F2” refers to a fluorine/fluoride containing compound, or a gasmixture, containing fluorine gas compound as well as other gases. Theanode and cathode chambers can be provided with gas inlets and outlets.Gas tight seals are enabled on each face (not shown) and between blocksby Viton or Kalrez O-rings. Power is applied to the electrodes directlythrough the Al blocks, from a power source (not shown), either at aconstant voltage (potentiostatic mode), or at a constant current(galvanostatic mode). The fluorine source can be F₂ in N₂, or other F₂containing gas mixtures. Unreacted F₂ from the cathode chamber can beneutralized in a scrubber, or can be recirculated for increasedefficiency. The anode chamber (not shown) can be purged with an inertcarrier gas, or can produce pure F₂ if the corresponding mass flowcontroller is stopped.

Example 4

Operation of a fluorine generation device in accordance with oneembodiment of the present invention. The process of operation is similarto that of Example 3, however the cathode material has to beelectrochemically active for the reduction of the fluorine precursor.For example, a preferred chemical for storing fluorine is NF₃. This canbe reduced at the cathode according to the reaction2NF₃+6e⁻→N₂+6F⁻releasing N₂ into the exhausted gas and F into the electrolyte. As inprevious example, F⁻ is transported to the anode and oxidized to F₂. Thecathode material can be a metal such as that used in previous example,preferably Pt powder, most preferably activated Pt (black Pt).

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, those skilled in the art willappreciate that various adaptations and modifications of the justdescribed preferred embodiments can be configured without departing fromthe scope and spirit of the invention. Moreover, the describedprocessing distribution and classification engine features of thepresent invention may be implemented together or independently.Therefore, the described embodiments should be taken as illustrative andnot restrictive, and the invention should not be limited to the detailsgiven herein but should be defined by the following claims and theirfull scope of equivalents.

1-23. (canceled)
 24. A solid state electrolytic device for removingfluorine from a semiconductor exhaust gas, comprising: a first andsecond electrode, wherein the first electrode is a cathode and thesecond electrode is an anode; a solid electrolyte disposed between theanode and cathode; and, a fluid-tight chamber that comprises an inletand fluid contact with at least one of the electrodes; whereby fluorineis removed from a fluorine-containing exhaust gas mixture produced bysemiconductor manufacturing, when the exhaust gas is supplied to the gasinlet.
 25. The device of claim 24, comprising a power source to applypower to the electrodes.
 26. The device of claim 24, comprising meansfor supplying an electric potential to the electrodes.
 27. The device ofclaim 24, wherein the electrodes each comprise a material selected fromthe group consisting of platinum, platinum alloy, gold, gold alloy,nickel, nickel alloy, palladium, palladium alloy, copper, copper alloy,silver, silver alloy, carbon and graphitic carbon.
 28. The device ofclaim 24, wherein the electrolyte is impermeable to gases.
 29. Thedevice of claim 24, wherein the electrolyte is permeable to fluorideions.
 30. The device of claim 24, wherein the electrolyte is selectedfrom the group consisting of PbSnF4, LaF₃ and doped LaF₃.
 31. The deviceof claim 24, wherein the fluorine gas mixture comprises one or moregases selected from the group consisting of HF, NF₃, F₂, CF₄ and SF₆.32. The device of claim 24, wherein the electrodes comprise fluid-tightseals on respective faces of the electrolyte.
 33. The device of claim24, wherein the electrolyte is deposited on a substrate.
 34. A methodfor removing fluorine from an exhaust gas produced by semiconductormanufacturing, comprising: providing a solid electrolyte positionedbetween an anode electrode and a cathode electrode, each electrode in aseparate fluid environment; supplying the semiconductor exhaust gas,containing fluorine, to one of the electrodes; and applying an electricpotential between the electrodes; and, whereby fluorine is removed fromthe semiconductor exhaust gas.
 35. The method of claim 34, wherein theelectrodes each comprise a material selected from the group consistingof platinum, platinum alloy, gold, gold alloy, nickel, nickel alloy,palladium, palladium alloy, copper, copper alloy, silver, silver alloy,carbon and graphitic carbon.
 36. The method of claim 34, wherein theelectrolyte is impermeable to gases.
 37. The method of claim 34, whereinthe electrolyte is permeable to fluoride ions.
 38. The method of claim34, wherein the electrolyte is selected from the group consisting ofPbSnF₄, LaF3 and doped LaF₃.
 39. The method of claim 34, wherein theexhaust gas comprises one or more gases selected from the groupconsisting of HF, NF₃, F₂, CF₄ and SF₆.
 40. The method of claim 34,wherein the exhaust gas is recirculated or neutralized.
 41. The methodof claim 34, wherein the providing step comprises: providing an anodechamber in fluid connection to the anode, and a seal at an interface ofthe anode and the anode chamber; and, a cathode chamber in fluidconnection to the cathode, and a seal at an interface of the cathode andthe cathode chamber.
 42. The method of claim 34, wherein the providingstep provides the electrolyte formed on a substrate.